Rotorcraft skid undercarriage and a rotorcraft including such an undercarriage

Abstract

The invention relates to a rotorcraft (21) comprising a fuselage (22) and an undercarriage (20) having skids (24, 25) interconnected by at least one cross-member (26, 27), together with connection means for connecting the cross-member to the fuselage and presenting angular stiffness that varies with varying sinking (E) of the undercarriage as a result of contact with the ground (23).

Description

[0001]The present invention relates to improvements to skid undercarriages for rotorcraft, and to rotorcraft including such an undercarriage.[0002]The technical field of the invention is that of manufacturing helicopters.BACKGROUND OF THE INVENTION[0003]In addition to allowing a rotorcraft to be maintained in a stable position or to slide on the ground, the undercarriage or landing gear has as its main function that of dissipating at least part of the energy of the impact that is caused by the rotorcraft landing.[0004]This energy is absorbed by friction against the ground, by deformation of the undercarriage, and of its connections with the airframe of the rotorcraft, and where appropriate by shock absorbers. Such deformation is made possible by the parts of the undercarriage being elastic.[0005]The rotorcraft standing on its undercarriage can be thought of as a suspended weight. The resulting mechanical system presents resonant modes of deformation that correspond to resonant frequ...

AI Technical Summary

Benefits of technology

[0022]Under such circumstances in particular, the first connection means preferably further comprise a resilient band member associated with each first saddle to co-operate therewith to surround the cross-member, while allowing the cross-member to move vertically relative to the saddle and inside the saddle, as is made possible by the elastic deformation of the band member which serves to keep the undercarriage in place when the rotorcraft is in flight.

[0028]In particular, an undercarriage is proposed in which the generally tubular cross-member (of closed profile) presents smaller second moment of area in a central portion than in two side (end) portions extending on either side of the central portion. This encourages “controlled” deformation of the cross-member, and in particular of its central portion; this increased capacity for deformation (elastic and plastic) of the cross-member serves both to reduce the (angular) stiffness in roll of the aircraft resting on its undercarriage, and also its stiffness along the vertical axis.

Problems solved by technology

When the undercarriage is subcritical, no frequency crossing occurs up to nominal speed, but a change in the weight, in the roll inertia, or in the position of the center of gravity can lead to a frequency crossover occurring close to nominal speed, thereby creating coupling that is explosive.

The undercarriages described in those documents are relatively complex and heavy.

Another unsolved problem is that of providing a skid undercarriage that is relatively unsophisticated while nevertheless reducing the load factor imposed on passengers during landing, as compared with rigid undercarriages.

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